A network storage, such as an NAS, has been increasingly used. Constant connection to the Internet in a computer has become common. Therefore, even when users access files in an NAS in a situation that most computers are placed in a closed area, such as a LAN, the computers are connected to the Internet.
This causes a problem that malicious software (hereinafter, referred to as malware) opens data, stored in the NAS, to the public on the Internet in a form that is not intended by a user.
In addition, there may also be a problem due to a careless, inappropriate operation, such as a case where a user misidentifies an actually public area on the Internet as a private work area and then places important private data therein or a case where a user establishes connection to a network while a folder that originally should not be open to the public remains open to the public.
There is a simple solution for the above problems, that is, to “directly unplug a LAN cable”; however, this requires unplugging a LAN cable of a router, or the like, so it is burdensome.
There is the following Patent Document related to a technique for preventing information leakage in a computer.
[Patent Document 1] Japanese Laid-open Patent Publication No. 2003-122615